Diabetic patients may fall into hypoglycemia during sleep (i.e., an episode of nocturnal hypoglycemia) (the term “hypoglycemia” generally refers to a state where the patient's blood glucose level drops to a level not higher than 70 mg/dl). For the purpose of making a diagnosis of the presence or absence of nocturnal hypoglycemia, a puncture device such as one disclosed in U.S. Patent Application Publication No. 2004-0260324 is used to puncture the skin of a subject to collect blood and measure the blood glucose level at night.
However, making a diagnosis of the presence or absence of nocturnal hypoglycemia in such a manner is based on a blood glucose level measured only at one time point during the night. For this reason, the diagnosis result is not fully reliable. Moreover, the subject is required to wake up at night for the collection of blood. This disturbs the subject's sleep.
As a solution to the above problems, it is proposed to make continuous diagnoses of the presence or absence of nocturnal hypoglycemia by using a device for continuously measuring glucose concentrations. For example, International Publication WO2002/015777 discloses a device including: electrodes through which a current is applied to the skin of a subject to cause electroosmosis of glucose in the subject's body; a biosensor for reacting with the glucose which electroosmotically moves from the skin and outputting a signal accordingly; and a microprocessor for reading a glucose concentration every twenty minutes from the outputted signal and storing the glucose concentration.
U.S. Pat. No. 6,424,847 discloses a glucose monitor system including: a glucose sensor to be inserted into subcutaneous tissue of a subject; and a glucose monitor for obtaining a signal from the glucose sensor at predetermined intervals, thereby measuring glucose concentrations in the subcutaneous tissue.
Unlike the method disclosed by U.S. Patent Application Publication No. 2004-0260324, the use of the device disclosed in International Publication WO2002/015777 or the system disclosed in U.S. Pat. No. 6,424,847 allows blood glucose levels of the subject to be obtained continuously. This improves the accuracy in diagnosis of the presence or absence of hypoglycemia.
However, the device disclosed in International Publication WO2002/015777, which includes the electrodes and the biosensor, needs to be worn on an arm of a subject. Also, the system disclosed in U.S. Pat. No. 6,424,847 requires the glucose sensor to be kept inserted in the skin of a subject. Thus, the subject has a burden of wearing a device if the method using the device of International Publication WO2002/015777 or the method using the system of U.S. Pat. No. 6,424,847 is employed. In particular, wearing such a device during sleep is a significant burden for the subject.